The present invention relates to a viscous fluid clutch adapted to drive an accessory device, such as a cooling fan, for an internal combustion engine.
Japanese Utility Model Application First Publication No. 3-26839 discloses a viscous fluid clutch adapted to drive a cooling fan for an internal combustion engine. This viscous fluid clutch includes relatively rotatable first and second drive members having a fluid shear space therebetween and which are cooperable with a fluid medium in the shear space to provide a shear-type fluid drive therebetween. In the viscous fluid clutch, an auxiliary reservoir is provided in addition to a main reservoir for storing fluid in order to decrease the level of fluid at rest and to avoid dragging of the first drive member upon starting to rotate the second drive member at cold engine.
Specifically, a housing is rotatably mounted to a drive shaft and a clutch plate is attached to the drive shaft. The housing includes a reservoir, an operating chamber and a pump outlet opening communicating between the operating chamber and the reservoir. The clutch plate includes an annular projection defining an annular space serving as the auxiliary reservoir. The housing has an annular recess accommodating the annular projection. The annular recess is defined by a cylindrical surface extending around the axis of rotation of the clutch plate. The annular projection of the clutch plate is formed with radial openings. During rotation of the clutch plate upon start at cold engine, the fluid medium is thrown radially outwardly from the auxiliary reservoir, owing to the centrifugal force, through the radial openings. In order to pump the fluid medium axially toward the operating chamber and then to the pump outlet opening, the annular projection has pump elements opposed to the cylindrical surface of the housing. Owing to this pump structure, there occurs transmission of drive to the housing. Besides, high precision machining is required, resulting in cost increase in manufacturing.
An object of the present invention is to improve a viscous fluid clutch of this type such that, without the pump, the fluid medium within the auxiliary reservoir flows quickly into the operating chamber with inducing the dragging phenomena.